The present invention relates generally to alternators and, more particularly, to improved alternators and methods for operating such alternators to improve alternator output current particularly at lower speeds. While the present invention is generally applicable, it will be described herein with reference to use in motor vehicles.
A conventional motor vehicle alternator includes a three phase stator winding with a rotor magnetically coupled to the stator and driven by the vehicle's internal combustion engine. As the rotor is driven, three phase power, generated at output connections of the stator winding, is rectified by a three phase diode rectifier bridge. Unfortunately, the output current and efficiency, both mechanical and electrical, of the alternator vary with the speed of the engine which is controlled for the mechanical requirements of the vehicle. At low speeds, the alternator output may be insufficient to provide the power needed to operate all electrical equipment of the vehicle while at high speeds, power generation is sufficient to far exceed these requirements.
The operating speed of an alternator used in the electrical system of a motor vehicle may be varied to overcome the noted inconsistencies between power generation and power requirements and to advantageously generate sufficient power for the motor vehicle when the engine is operating at a low speed. For example, a variety of two speed alternators operable at a higher speed for low speed operation of the corresponding motor vehicle engine are known.
While such alternator control arrangements are useful in providing adequate power at low engine speeds or for protecting alternators at high engine speeds, they rely on mechanical speed change devices which can be unreliable.
Accordingly, there is a need for an improved alternator which is reliable and does not rely on mechanical speed changing devices to improve alternator operation and arrangements for controlling operation of such an alternator for example in a motor vehicle.